As liquid enclosing type vibration isolating mounts for supporting a vibration generating body such as an automobile engine, there have conventionally been proposed various kinds of structures.
For example, there is shown in FIG. 14 a two chamber liquid enclosing type vibration isolating mount 150 which is constructed such that a cylindrical metal 152 and a fixing metal 159 are connected by a vibration isolating base member 153 made of elastic rubber, a diaphragm 154 made of a rubber membrane and a partition member 155 located inside the former are sealably fixed to the open end of the cylindrical metal 152 opposing to the vibration isolating base member 153 and an inner space between the vibration isolating base member 153 and the diaphragm 154 is divided into two liquid chambers 157 and 158 communicating with each other through an orifice path 156 whereby the vibration damping function and the vibration insulating function can be performed by the liquid flow effect by the orifice path 156 and the vibration isolating effect by the vibration isolating base member 153. Note that reference numeral 151 designates a cylindrical base metal for holding the cylindrical metal 152 therewithin and in some case both metals 151 and 152 are formed integral with each other.
Conventionally, it has been usual that the partition member 155 of the above-described vibration isolating mount 150 is either a molded aluminum, a molded synthetic resin or a product of machining of metal, and the orifice path 156 is in the form of an annular groove 160 provided on the outer peripheral surface of the partition member 155.
However, where the partition member 155 is a molded goods or a product of machining of metal, there arises the problem that the manufacturing cost is high.
Therefore, a first object of the present invention is to reduce the cost of manufacturing the above-mentioned two chamber liquid enclosing type vibration isolating mount.
Now, where the vibration isolating mount 150 of the above-described structure is used to support an automobile engine, the upper fixing metal 159 is usually fastened to the engine-side bracket.
In using the above vibration isolating mount 150, the vibration isolating base member 153 flexes by load of the engine or the like. When the vibration isolating base member 153 is fixed to the cylindrical metal 152 keeping a required space from the partition member 155 as described above, the vibration isolating base member 153 flexes and deforms within the entire inner portion of the cylindrical metal 152. Consequently, the amount of deflection of the vibration isolating base member 153 at the time of receiving the above-mentioned load increases resulting in increasing the amount of creeping thereof due to the deflective deformation by that degree so that the vibration isolating base member 153 can not have a sufficient degree of durability.
Further, in the vibration isolating mount of the above type, each of the upper fixing metal 159 and the basic metal 151 fixed to the frame of the chassis are provided with a stopper. When the amount of displacement due to vibration is large the stoppers come into contact with each other so as to prevent the vibration isolating mount from displacing up and down largely due to the vibration of the engine or the like.
For example, in the case of FIG. 14, the upper fixing metal 159 is provided at a part thereof with a projection 159a covered with the vibration isolating base member 153, and an inner end 151a of an upward extension of the base metal 151 is formed to serve as a stopper with which the above-mentioned projection 159a comes into elastic contact (usually a clearance is kept therebetween) when the amount of upward displacement of the mount due to vibration is large, where by a further displacement of the mount is controlled.
Usually, such vibration isolating mount is made to have a substantially constant stopper clearance with respect to a certain load in proportion to the static spring constant of the vibration isolating base member but where an automobile engine or the like is supported by a plurality of mounts, the parts of the engine load allotted to the mounts differ depending on the points of use of the mounts and due to this nonuniformity of the allotted amounts of the load, the stopper clearance for each mount becomes nonuniform resulting in the generation of hammering sounds.
However, to increase the static spring constant of the rubber member forming the vibration isolating base member results in increasing the dynamic constant thereof at the same time so that the spring characteristic deviates to a great degree with an unfavorable result of failing to obtain an expected vibration isolating effect.
Therefore, a second object of the present invention resides in that in the above-described two chamber liquid enclosing type vibration isolating mount, the static spring constant of the vibration isolating elastic base member can be made to increase without increasing the dynamic spring constant, the deflective deformation of the vibration isolating base member, especially the downward deflective deformation, is reduced to thereby reduce the amount of creeping due to such deflective deformation so that the durability of the mount is enhanced and the stopper clearance is less affected by the deformation.
On the other hand, there is the problem that when the partition member 155 is made of a rigid material only as in the case of the vibration isolating mount 150, the dynamic constant is generally high and the noise transmissivity is also high so that the interior sounds such as muffled sound or transmitting sound go high.
In order to solve this problem, as shown in FIG. 15, it is contemplated to provide a rubber membrane 162 at the center of the partition member 155. Where such rubber membrane 162 is provided, there is a dynamic spring constant reducing effect in a frequency domain of about 100-300 Hz when compared to the use of the partition member made of the rigid material only. However, since the thickness of the rubber membrane 162 is constant in the radial direction, the dynamic constant around a frequency of 350 Hz becomes high so that it is not possible to reduce the dynamic spring constant in a high frequency domain over a wide range of 100-500 Hz.
Therefore, a third object of the present invention resides in that in the two chamber liquid enclosing type vibration isolating mount, the dynamic spring constant is reduced in a high frequency domain over a wide range of 100-500 Hz to thereby reduce the generation of muffled sound or transmitting sound.